Real-world Results: How the FA24 Engine Performs After Upgrading to a GReddy Turbo Kit

The Subaru FA24 engine has carved a reputation as a stout, modern flat-four that strikes a smart balance between daily practicality and genuine performance potential. Found in models such as the Subaru Ascent, Outback XT, and the latest WRX (2022+), this 2.4-liter powerplant delivers around 260 horsepower and 277 lb-ft of torque from the factory. For enthusiasts hungry for more, aftermarket turbocharging is an obvious path forward. Among the most popular and proven solutions is the GReddy Turbo Kit. But what does the upgrade actually feel like on the road and at the track? This article breaks down real-world dyno numbers, driving impressions, reliability considerations, and everything you need to know before bolting on a GReddy turbo system.

Understanding the FA24 Engine

Introduced in 2019, the FA24 is Subaru’s latest evolution of its boxer engine family. It succeeds the FA20 (used in earlier WRX and BRZ models) with a larger displacement, stronger block, and improved thermal management. Key specifications include:

  • Displacement: 2,387 cc (2.4 liters)
  • Configuration: Horizontally opposed flat-four
  • Valvetrain: Dual overhead camshafts, chain-driven
  • Stock compression ratio: 10.3:1 (WRX) or 10.6:1 (Ascent/Outback XT)
  • Fuel system: Direct injection
  • Factory power: ~260 hp / 277 lb-ft (WRX)
  • Redline: 6,450 rpm (WRX)

The FA24 features a closed-deck design with thicker cylinder walls compared to the FA20, giving it a higher inherent strength threshold. The factory turbocharger on the WRX is a twin-scroll unit that spools quickly but runs out of steam around 5,500 rpm. This is where an upgraded kit like GReddy’s shines—by flowing more air and sustaining boost across a wider rev range.

For a deeper technical background on the FA24, Subaru’s official engine page provides a good overview.

The GReddy Turbo Kit: Components and Design Philosophy

GReddy has been a leading name in Japanese turbo systems for decades, and their FA24 kit is no exception. The kit is engineered as a complete bolt-on solution, meaning it replaces the factory turbocharger, intercooler, exhaust downpipe, and intake plumbing without requiring custom fabrication. Core components include:

Turbocharger Core

The kit centers on a GReddy TD06-25G or T67-25G single-scroll turbocharger (depending on version). These are journal-bearing units with a billet compressor wheel, capable of supporting up to 450 wheel horsepower on pump gas and over 500 hp with E85. The turbine housing is available in 8 cm² or 10 cm² AR options, allowing tuning for faster spool or top-end flow.

Intercooler and Piping

A bar-and-plate front-mount intercooler replaces the factory top-mount unit. This reduces intake air temperatures significantly—critical for sustained boost on a turbocharged flat-four. The kit includes mandrel-bent aluminum piping with silicone couplers and T-bolt clamps.

Exhaust Manifold and Downpipe

The cast iron exhaust manifold is designed to flow evenly to the turbo flange. The downpipe features a 3-inch outlet with a catalytic converter option for emissions compliance. A 3-inch full exhaust system is recommended but not included.

Fuel System and Tuning

GReddy supplies a high-flow fuel pump and larger injector capacity (optional on some versions) alongside a plug-in ECU tune from Cobb or ECUTEK. The tune includes a custom calibration for boost levels around 12–14 psi on 91 octane fuel, with higher boost maps available for race gas.

For full specifications, visit GReddy's official turbo kit page.

Real-World Performance Results: Dyno Numbers and Acceleration

Enthusiasts who have installed the GReddy kit on their FA24-powered Subarus report impressive gains. Below are representative figures from independent dyno tests and user logs:

  • Stock WRX (FA24): 245–255 whp / 250–260 wtq (mustang dyno)
  • GReddy kit (91 octane, 12–13 psi): 350–360 whp / 370–390 wtq
  • GReddy kit (93 octane, 14–15 psi): 380–400 whp / 410–430 wtq
  • GReddy kit (E85, 18–20 psi): 430–460 whp / 460–500 wtq

The torque curve stands out: peak torque arrives around 3,800 rpm and stays flat past 6,000 rpm. That’s a massive improvement over the stock turbo’s drop-off after 5,500 rpm.

Drag Strip and 0–60 Times

With a proper launch and sticky tires (275/35R18 or larger), a GReddy-equipped FA24 WRX can hit 60 mph in 3.6–3.9 seconds and run the quarter-mile in 11.8–12.2 seconds at 119–122 mph. On street tires, expect 0–60 in 4.1–4.5 seconds. By comparison, a stock WRX runs the quarter in about 13.4 seconds at 102 mph.

Driving Experience: What Changes After the Install

Numbers only tell part of the story. Behind the wheel, the transformation is dramatic.

Spool and Throttle Response

The GReddy’s larger turbine creates a slight trade-off: initial spool is delayed compared to the tiny factory twin-scroll. On a 2.4-liter engine, significant boost builds by 3,200 rpm (versus 2,800 rpm stock). The delay is minor and is more than compensated for by the massive mid-range punch. Once boost hits, it pulls relentlessly to redline.

Power Band and Daily Usability

On the street, the kit behaves well. The car remains docile below 3,000 rpm, making it easy to drive in traffic. Above that, the throttle becomes lively. The broad torque plateau means fewer downshifts are needed for highway passing. The engine note gains a deeper, more urgent timbre, but the cabin remains quiet enough for long trips if the exhaust is kept stock-muffled.

Handling and Traction

With 400+ lb-ft of torque on tap, traction becomes an issue—especially in first and second gears. Larger tires and upgraded suspension (coilovers, sway bars) are recommended. The FA24’s front-heavy layout (even with a flat engine) means the LSD differential benefits from a higher bias oil or a limited-slip upgrade. Many drivers report that the car understeers less with the extra power if throttle is applied mid-corner.

Reliability and Supporting Modifications

The FA24 is a robust engine, but adding 50–70% more power demands careful attention. Here are critical factors to consider before and after the GReddy install:

Engine Internals

Stock pistons and rods are forged on the FA24 WRX, but the compression ratio (10.3:1) limits safe boost on pump gas. For power levels above 400 whp, a lower compression set of pistons (9.5:1 or even 9.0:1) is strongly advised. The GReddy kit can reach 450 whp on stock internals if fuel quality and tuning are meticulously controlled, but longevity is compromised.

Fuel System Upgrades

The direct-injection system supports moderate power, but at 400+ whp, supplemental port injection (PI) or larger direct injectors are needed to maintain fuel pressure. GReddy’s kit includes a high-flow pump, but a PI setup is an additional investment.

Oil and Cooling

Turbocharging increases heat load, particularly on the oil. An oil cooler (setrab or similar) is mandatory for track use. The FA24’s factory oil pan is adequate for street use; a baffled pan is recommended for sustained high-grip cornering. The intercooler included in the kit keeps charge air temperatures in check, but for aggressive tuning, a larger radiator and upgraded fan shroud help.

Clutch and Transmission

The stock clutch on the FA24 WRX begins slipping around 350 lb-ft. A stage 2 or stage 3 clutch (e.g., ACT, Exedy) is necessary for upgraded turbo kits. The six-speed manual gearbox (STI version or WRX’s own) can handle 400 whp, but synchros may wear faster with aggressive shifting. The CVT-only Ascent/Outback XT models are not recommended for this kit without extensive transmission upgrades.

A forum thread on Subaru101’s FA24 reliability discussion provides firsthand owner experiences.

Comparing the GReddy Kit with Other Options

The FA24 aftermarket has grown quickly. GReddy’s main competitors include Garrett and HKS kits, as well as the stock turbo that can be modified with a larger compressor wheel. Here’s how GReddy stacks up:

  • Garrett GTX3071R kit: Slightly faster spool than GReddy but lower top-end potential. More expensive.
  • HKS GTII 7460 kit: Similar design, but HKS uses a ball-bearing turbo—spool is quicker but peak power is slightly lower.
  • Stock turbo upgrade (TD04 hybrid): Budget option yielding 300–330 whp. Not comparable to GReddy’s 400+ whp capability.
  • Full race kit (Custom): Can exceed 550 whp but requires fabricated manifold, standalone ECU, and forged internals.

GReddy hits the sweet spot for enthusiasts wanting a reliable 400 whp daily driver that can still pass emissions (with the catted downpipe) and retain factory drivability.

Cost Breakdown and Installation Considerations

The GReddy turbo kit for FA24 typically retails between $4,500 and $5,500 depending on the version and included options. Installation labor adds another $1,000–$1,500 if you’re not turning wrenches yourself. Supporting modifications (clutch, intercooler, fuel system) can add $2,000–$4,000. A reasonable total budget for a safe, reliable build is $8,000–$12,000.

Installation is a straightforward weekend job for experienced enthusiasts. The kit comes with detailed instructions and bolts directly to the existing engine mounts. Clearances are tight on the passenger side, but no cutting or welding is required. The ECU reflash takes about 20 minutes with the included COBB Accessport or ECUTEK cable.

Is the GReddy Turbo Kit Worth It?

If you own an FA24-powered Subaru and feel the stock turbo runs out of breath too soon, the GReddy kit delivers a transformation that few other bolt-on modifications can match. The power gains are substantial, the torque curve is broad and usable, and the overall driving experience becomes genuinely exhilarating. With proper supporting mods and a conservative tune, the FA24 can handle the extra power for tens of thousands of miles.

That said, it’s not a plug-and-play upgrade for everyone. The added cost, maintenance requirements, and potential impact on daily comfort and fuel economy should be weighed carefully. But for those who crave real-world performance on both road and track, the GReddy turbo kit for the FA24 is one of the most rewarding investments you can make.

For a full list of install guides and dyno sheets, check out threads on iWSTI and the GReddy technical support page. The FA24 platform is still young, but with the right turbo kit, its potential is already being unlocked by thousands of enthusiasts worldwide.